When wiring on a semiconductor device is formed, first, a barrier layer and a conductor layer are formed in turn on an insulator layer having trenches. Then, at least the portion of the conductor layer positioned outside the trenches (the outside portion of the conductor layer) and the portion of the barrier layer positioned outside the trenches (the outside portion of the barrier layer) are removed by chemical mechanical polishing. This polishing for removing at least the outside portion of the conductor layer and the outside portion of the barrier layer is usually performed in a first polishing step and a second polishing step. In the first polishing step, part of the outside portion of the conductor layer is removed in order to expose the upper surface of the barrier layer. In the following second polishing step, at least the remainder of the outside portion of the conductor layer and the outside portion of the barrier layer are removed in order to expose the insulator layer and obtain a flat surface.
A polishing composition used in such polishing for forming wiring on a semiconductor device generally contains a polishing accelerator, such as an acid, and an oxidizing agent, and further contains polishing abrasive grains as required. In addition, in order to improve the flatness of an object-to-be-polished after polishing, the use of a polishing composition to which a water-soluble polymer is further added has also been proposed. For example, Patent Document 1 discloses the use of a polishing composition containing an anionic surfactant, such as ammonium polyoxyethylene lauryl ether sulfate, a protective film-forming agent, such as benzotriazole, and a nonionic surfactant, such as a polyoxyethylene alkyl ether. Patent Document 2 discloses the use of a polishing composition containing an epihalohydrin-modified polyamide. Patent Document 3 discloses the use of a polishing composition containing a chemically modified gelatin having an amino group modified with a carboxylic acid.
When wiring on a semiconductor device is formed by chemical mechanical polishing, unintended inconvenient depressions may be formed on the sides of the formed traces particularly when the conductor layer is formed of copper or a copper alloy. It is considered that the depressions on the sides of traces are formed mainly because the surface of the portions of the conductor layer positioned near boundaries with the insulator layer is corroded during polishing. Even if the conventional polishing compositions as described above are used, it is difficult to prevent the depressions on the sides of the traces from being formed.